This invention relates to the deposition of compounds on substrates, and, more particularly, to laser and thermal assisted chemical vapor deposition of mercury-containing compounds.
The deposition of compounds on substrates is one of the standard manufacturing techniques in constructing a variety of electronic, optical, and opto-electronic devices. Such techniques usually call for the deposition of thin layers of a substance onto a substrate, the layer usually being less than 0.001 inches thick. The crystalline perfection of the resulting structure is usually critical to the successful functioning of the final product, and various techniques have been selected, modified, and optimized for use in particular applications.
One of the commonly used deposition techniques is chemical vapor deposition. In metal organic chemical vapor deposition (MOCVD), each metal to be codeposited upon the substrate is combined into an organic molecule, and the two (or more) types of reactant organic molecules are stored in reservoirs. Appropriate amounts of the reactant molecules are mixed into a carrier gas stream, which is then introduced into a reaction chamber that contains the substrate. The substrate is heated to aid in decomposing the organic molecules, and to aid in their deposition on the substrate surface. At normal deposition temperatures of 300.degree. C. or greater, the metal organic molecules decompose at the surface of the substrate, depositing their metal atoms onto the surface and freeing the organic residues to be carried away in the flowing gas stream.
Conventional MOCVD processes require high temperatures, which can result in degraded microstructures and excessive interdiffusion in the deposited layer on the substrate, and in the substrate itself. To reduce the adverse effect of elevated temperatures on the final structures, a beam assisted variant of MOCVD has been developed. In assisted MOCVD, a high energy field is supplied to the metal organic vapor at the surface of the substrate. The beam imparts energy to the vapor, which assists in its decomposition at a lower temperature than possible with unassisted MOCVD.
One class of industrially important compounds deposited by MOCVD is mercury-containing compounds such as mercury telluride (HgTe) and mercury cadmium telluride (HgCdTe). These materials are deposited in thin films less than 0.001 inches thick, and in this form absorb impinging infrared energy to produce an electrical signal. The compounds can therefore be used as infrared detectors.
Such mercury-containing compounds are normally deposited by MOCVD from a mixture of dimethylmercury and diethyltellurium. When the deposition is unassisted and at a substrate temperature of greater than 300.degree. C., there is extensive interdiffusion and degradation of the structure. When beam-assisted MOCVD is used, a lower temperature is possible, but there remain significant problems with the resulting structure. One problem is that the mercury content of the structure is low, another is the inclusion of carbon contaminants in the deposited layer, and the third is a poor surface morphology.
There therefore is a need for an improved beam-assisted chemical vapor deposition technique for compounds containing mercury, that achieves the benefits of low-temperature deposition but does not exhibit the deficiencies mentioned above. The present invention fulfills this need, and further provides related advantages.